Misaligned Sensors: If the garage door sensors are misaligned, the door might not close properly. Adjust the sensors so that they're facing each other and aligned correctly.

Lubrication: Squeaky or noisy garage doors can often be fixed by applying lubricant to the moving parts, such as hinges, rollers, and tracks.

Loose Hardware: Over time, nuts and bolts can become loose. Check and tighten any loose hardware, such as brackets, hinges, and track bolts.

Replacing Batteries: If your remote control or keypad is not working, check and replace the batteries.

If your door only goes down 3-6 inches and reopens check to see if the safety sensors are obstructed. Try to align the photo eyes (located at the bottom left and right side of the door) until both lights are solid or clean the lens from dirt or moisture.

If your door reaches the bottom of the floor and reopens or stops short grab a ladder and check the operators limits and force. depending on the unit it my be adjusted manualy or digitaly 

If your door only opens about 3-6 inches it maybe a broken spring & requires a professional technician to repair it. Unplug the motor to prevent accidental damage.

 if your door doesn't open at all try releasing the emergency release latch (usually a red string) and try to lift the door manually. Try replacing remote or keypad batteries or confirming there is power to the unit.